54 THE SCALLOP FISHERY 



which the scallop is often subjected. If it were not for some means of 

 holding fast to the eel grass or other supports, the heavy storms would 

 wash the small animals ashore. So possibly this power has been devel- 

 oped by natural selection for the protection of the scallop. Also, nature 

 has acted wisely in making the attachment and climbing powers of the 

 scallop supplementary, as the climbing habit is necessary to enable 

 the scallop to reach a place of attachment, or, when attached, to find a 

 better location. 



Spat Collecting. The attachment period in the life of the scallop 

 naturally offers the best opportunity for the capture of " seed." When 

 this period of life is reached in the case of the oyster, the planter puts 

 into the water large quantities of shells, on which the young oyster may 

 " set " or permanently attach itself by a calcareous fixation. The 

 scallop, unlike the oyster, has no power of calcareous fixation, and the 

 byssus is not a* permanent attachment. If found desirable, old nets, 

 frayed rope, boxes, etc., hung in a moderate current, should furnish an 

 excellent means of collecting spat. Although scallop Iarva3 were plenti- 

 ful in the water, no natural set on the eel grass occurred during the 

 summer of 1906 in the Powder Hole at Monomoy Point. Nevertheless, 

 on boxes and frayed rope, lowered for spat collecting from a raft, 1,200 

 small scallops were obtained in a few square feet of surface. At the 

 present time there is no distinct need of spat collecting, as " seed " is 

 superabundant in many localities. The young dissoconch scallops usu- 

 ally are attached by one byssal thread. 



LOCOMOTION. 



The young scallop depends greatly upon its powers of locomotion to 

 enable it to maintain the struggle for existence, to seek new fields and 

 to escape its enemies. Early movement is shown by the swimming of 

 the ciliated embryo, an entirely distinct process from the same function 

 in the adult scallop. Between intervals of attachment it moves by 

 crawling with the foot either along the level or clinging to perpendicular 

 surfaces, a considerably slower method than the earlier habit. Later, 

 the swimming powers of the adult gradually appear, although the 

 scallop still maintains its crawling powers. There is a gradual develop- 

 ment in its methods of locomotion comparable to changes in its life, 

 each of which are adapted to the special needs of the animal. 



Crawling. The scallop, long before it lost the faculty of swimming 

 with its foot, had the power of crawling, although it did not wholly rely 

 upon this method. When the body became too heavy to swim success- 

 fully with the foot, the animal depended entirely upon the latter means 

 of locomotion. Later, when the swimming habits of the adult made their 

 appearance, the young scallop used both, assisting the act of crawling 

 by shooting a stream of water from the posterior edge of the shell in 

 unison with the contraction of the foot. Crawling is accomplished by 

 three muscular actions of the foot, extension, holding and contraction 



